Sunburn is an acute dermatitis which occurs when sunlight, particularly UV-rays, has been allowed to act excessively over the permissible physiological range of the skin, and is expressed as erythema (sunburn) and blackening (suntan). That is, although the intensity of the sunburn and the lapse thereafter will generally vary in accordance with the quantity and intensity of the UV-ray dosage generally acting on the skin, first a congestion of capillaries within the skin will occur, followed by erythema (sunburn) accompanied by edewa. After several days, the inflammation disappears, simultaneously with a disappearance of the erythema, and a melanin dye is deposited within the skin to cause a blackening (suntan) of the skin.
UV-rays are classified by wavelength, i.e., into a short wavelength UV-ray region of 280 nm or lower (UV-C), a medium wavelength UV-ray region of 280 to 320 nm (UV-B), and longer wavelength UV-ray region of 320 to 400 nm (UV-A), but since UV-rays having a wavelength of 290 nm or lower are absorbed by the ozone layer in the atmosphere, and do not reach ground level, only the UV-rays having a wavelength of from 290 to 400 nm (UV-B and UV-A) are biologically important. Namely, UV-rays having a wavelength of 290 to 320 nm (UV-B) are the primary cause of acute erythema (sunburn), and are known as erythema region UV-rays, and UV-rays having a wavelength of 320 to 400 nm (UV-A) are known as the blackening region UV-rays, since these UV-rays promote blackening (suntan) of the skin.
In recent years, UV-ray absorbers, etc., have been developed and various cosmetics for preventing sunburn of the human skin have been developed and are widely used. However, the intensity of UV-rays is greatly influenced by the season, the time of day, and the weather, among other factors. Accordingly, as a counter-measure against sunburn, it is necessary to measure the irradiated dose of UV-rays by a suitable and simple means. Various methods for this measurement have been developed in the prior art. For example, dosimeters for determining an irradiated dose from fluorescent amounts or absorbance generated corresponding to the irradiated dose when a UV-ray with a specific wavelength is irradiated, are known.
However, these prior art methods of measuring a UV-ray does require great skill and a considerably long measurement time when measuring such a dose, and the measuring devices concerned have a drawback in that they are complicated and expensive.
In this connection, compositions which are discolored by the irradiation of UV-rays are disclosed in Japanese Patent Publication (Kokoku) No. 40-17986 (photosensitive composition), Japanese Patent Publication (Kokoku) No. 44-22941 (photosensitive printing material), and Japanese Unexamined Patent Publication (Kokai) No. 60-89352 (UV-ray discoloration sheet), among others, but all of these compositions undergo discoloration by irradiation of UV-rays within an extremely short time, and therefore, although the presence of UV-rays can be determined by the color change, it is impossible to measure the irradiation dose of UV-rays.